一种基于分布式发射天线的差分空时调制方法

在基于分布式发射天线的多入多出(MIMO)系统中,由于各发射天线的发射信号不同时到达接收端,用于信道估计的导引设计及发射方法存在一定困难。针对这一问题,该文提出一种无需信道估计的分布式MIMO差分编码及检测方法:发送端将发射矩阵进行相位差分调制后发射,接收端利用前后接收量判断相位信息恢复出发送端数据信息。该方法频谱效率与V-BLAST相同,适用于任意发射天线数和接收天线数,且不要求接收天线数大于发射天线数。仿真结果表明,在不同信道传播时延情况下,误码率性能不同。     

分布式发射天线V-BLAST信号的排序干扰抵消检测

针对V-BLAST信号通过分布的发射天线进入信道,该文提出了一种由于发射天线地域上的分布性引起的各发射天线发射信号不同时到达接收天线的V-BLAST排序干扰抵消(Order Interference Cancellation, OIC)检测算法。计算机仿真显示,该算法适用于任意个数的接收天线,在较高信噪比(20dB)的条件下,性能优于直接迫零算法3dB以上。在相同信噪比条件下,分布发射天线V-BLAST的排序干扰抵消检测算法比集中发射天线V-BLAST的排序干扰抵消检测算法有着更好的性能。     

一种分布式MIMO信号的发射与检测方法

在 V-BLAST结构的分布式多输入多输出(MIMO)系统中,针对发射天线地域分布所引起的发射符号异步到达接收天线的问题,给出了一种分布式 MIMO 系统的信号发射与检测方法。在慢衰落信道中,该方法利用接收端反馈的信道状态信息,采用几何平均分解(GMD)构建等对角的上三角矩阵,消除子信道间增益的不平衡。在莱斯衰落信道下的计算机仿真表明,与已有 QR分解的分层算法相比,该检测方法能够显著提升系统的误码性能。     

自适应比特功率分配的MIMO OFDM系统性能

该文首先分析了多天线发射和接收(MIMO)的OFDM系统模型。然后针对在多径衰落信道下,OFDM中一些深度衰落的子载波降低了系统性能。该文把一般多载波系统中的自适应比特功率分配算法推广应用到多天线OFDM系统中。同时研究了自适应MIMO OFDM系统的频谱效率。仿真结果表明,自适应比特功率分配提高了MIMO OFDM的误比特率性能和频谱效率。     

基于迫零检测的异步V-BLAST最优发射功率分配

由于异步发射V-BLAST各路子流的符号在时间上未对齐,同步V-BLAST所采用的逐符号功率分配方法不再适用。针对这个问题,该文提出了一种以块平均误比特率为优化目标,逐符号块进行功率分配的方法。该方法首先计算每个符号的瞬时信噪比,然后求出异步符号块的平均误比特率,最后求解优化问题得到各天线的最优发射功率值。平坦瑞利衰落信道下的仿真表明:两发两收、BPSK调制、迫零检测的异步V-BLAST,误比特率为10-3时最优功率分配有2dB的性能改善。     

分布式STBC-OFDM交织深度优化

该文在分布式发射天线场景下,考虑多径瑞利衰落信道,针对每个天线上分别采用交织分组子载波功率扩展的STBC-OFDM链路,提出了一种交织深度优化方法:根据分布式信道的多径数和多径时延,以最小化成对错误概率上界为目标,设置交织子载波分组的交织深度。在两发一收STBC, BPSK调制,由M.1225步行测试信道A, B组成的分布式场景下仿真,结果表明:当误比特率为10-5时,与传统方法相比,该文方法有1.5 dB的功率节省。     

基于迫零检测的分布式发射天线V-BLAST OFDM系统中的载波频偏补偿

 在采用分布式发射天线的垂直贝尔实验室分层空时结构(V-BLAST)正交频分复用(OFDM)系统中,由于各发射天线与接收机之间的载波频偏(CFO)均可能不同,传统系统中针对单个频偏的简单补偿方法不再适用。不同于已有的使用高复杂度矩阵求逆运算的线性频域均衡方法,本文利用迫零(ZF)检测的固有特性,提出一种适用于低时延扩展多径信道的无需矩阵求逆运算的载波频偏补偿方法。仿真结果表明,在ITU-R M.1225信道模型的三种低时延扩展测试环境下,使用本文所提频偏补偿方法进行频偏补偿能有效改善系统误符号率(SER)性能。     

基于分布式天线协同的OFDM粗定时同步方法

在频率选择性衰落信道中,两根分布式接收天线接收来自单天线发射机的发射信号。利用两根分布式接收天线的协同,提出了一种协同的粗定时同步方法。该方法在不增加各分布式接收天线预定虚警概率的情况下,通过两根分布式接收天线的协同,避免了部分漏检情况的发生。分析和仿真结果表明,提出的方法可以改善OFDM系统粗定时同步的正确检测和漏检性能。     

分布式MIMO系统中最优检测的简化算法

在V-BLAST结构的分布式MIMO系统中,针对发射天线地域上的分布性所引起的发射符号异步到达接收天线的问题,提出了一种接近最优检测性能简化算法。该算法首先遍历部分码元符号,且每次遍历时都使用分布式排序干扰抵消算法检测剩余符号,然后对得到的符号候选集进行搜索,恢复发送信号。莱斯衰落信道下的计算机仿真表明,该算法对接收端天线数目没有要求,且在获取接近最优检测性能的同时,有效地降低了计算复杂度。     

线型小区中V-BLAST两根分布发射天线的位置优化

在分布式发射天线多输入多输出(MIMO)系统中,不同的发射天线位置将影响系统的性能。针对这一问题,该文在考虑了传播时延、路径损耗、阴影衰落、小尺度衰落和高斯白噪声的基础上研究了V-BLAST两根分布式发射天线在线型小区的平均误码率(AABER)。理论分析表明存在一个关于小区中心对称的位置使得AABER性能最优,这一位置可以通过数值计算的方法得到。仿真结果验证了理论分析的正确性。     

线形小区中分布式天线协同的定时捕获改进方法

不精确的定时捕获造成分布式天线系统性能的严重下降,现有的改善分布式天线系统定时捕获性能的方法存在诸多不足。为进一步提高分布式天线系统定时捕获时的正确捕获概率,提出了一种基于分布式天线协同的定时捕获方法。该方法针对线形小区的平坦瑞利衰落信道场景,利用两根分布式接收天线接收来自单天线移动台的发射信号;随后,推导了两分布式接收天线的时延差先验信息,建立了协同定时捕获的协同条件;最后,根据门限检测方法在协同条件下进行定时捕获。分析与仿真结果表明,在定时捕获时,无论移动台处于协同区域的哪个位置,提出方法均能有效改善各分布式接收天线的正确捕获概率。     

Analysis of Differential Orthogonal Space–Time Block Codes Over Semi-Identical MIMO Fading Channels

We study the performance of differential orthogonal space-time block codes (OSTBC) over independent and semi-identically distributed block Rayleigh fading channels. In this semiidentical fading model, the channel gains from different transmit antennas to a common receive antenna are identically distributed, but the gains associated with different receive antennas are nonidentically distributed. Arbitrary fluctuation rates of the fading processes from one transmission block to another are considered. We first derive the optimal symbol-by-symbol differential detector, and show that the conventional differential detector is suboptimal. We then derive expressions of exact bit-error probabilities (BEPs) for both the optimal and suboptimal detectors. The results are applicable for any number of receive antennas, and any number of transmit antennas for which OSTBCs exist. For two transmit antennas, explicit and closed-form BEP expressions are obtained. For an arbitrary number of transmit antennas, a Chernoff bound on the BEP for the optimal detector is also derived. Our results show that the semi-identical channel statistics degrade the error performance of differential OSTBC, compared with the identical case. Also, the proposed optimal detector substantially outperforms the conventional detector when the channel fluctuates rapidly. But in near-static fading channels, the two detectors have similar performances     

Fading characteristics of distributed antennas

Distributed antennas have been suggested as a possible method of providing reliable coverage for indoor wireless communication systems. A potential problem with them however is the possibility of increased channel fading caused by interference between individual antennas in the distributed antenna. The authors present measurement and simulation results of the fading characteristics of distributed antennas to exactly determine whether they will play a significant role in the coverage provided. and how they will affect system design     

分布式MIMO系统发送天线选择与预编码联合设计

为了抑制多用户分布式多入多出(MIMO)系统中的同道干扰(CCI),使系统同时服务于更多用户,提出一种发送天线选择与预编码的联合设计方法。该方法立足于分布式MIMO系统基站端天线较多的特点,将下行发送天线选择与信漏噪比(SLNR)预编码相结合,通过为用户选择不同天线,从根本上减少CCI;在为每个用户选择天线时,先以信道子矩阵的迹为依据进行端口选择,再采用逐减的方法选择使SLNR损失值最小的天线,以保证每个用户对其他用户的干扰尽量小,从而达到进一步抑制CCI的目的。复杂度分析和仿真结果表明,该方法在具有较低复杂度同时,其容量性能仍可逼近最优算法;较之单纯的SLNR预编码,在相同的容量性能约束下,其能够有效增加系统同时服务的用户数。     

基于Schmidt正交化的多天线选择复用

该文从提高信道传输有效性的角度,提出了一种新的多天线选择发送策略--贪婪搜索(GS)法,使用这种方法挑选出使容量最大化的发送天线组合作为传输信号的天线。此法在结合注水(waterfilling)法进行天线功率分配的情况下,与理想的全天线注水法相比,可以减小发射机的复杂度,在独立信道下传输容量略有损失,在相关信道下可以提高传输容量,并且所付出的代价是仅需要对信道矩阵进行Schmidt正交化变换。这种方法一般用于信道矩阵列不满秩,即发送端天线数大于接收端天线数,发送端已知信道矩阵的情况(与注水法结合)或者接收端已知信道矩阵的情况(等功率分配)。     

Optimally Interleaved Signals for SFN

This paper focuses on how designing transmit signals improves performance of single frequency networks (SFNs), employing multiple distributed transmit antennas. Considering the effect of multipath fading, pairwise error probability conditioned on shadowing is derived to show that the achievable diversity order of SFNs increases as the number of resolvable channel taps between transmit and receive antennas increases. One transmit signal based on interleaved-partition subcarrier grouping is proposed to obtain the achievable diversity order. Further, we show that different interleaving methods result in different performance due to asynchronous delays caused by unequal distances between distributed transmit antennas and mobile receivers. To optimize the proposed transmit signal, one interleaving scheme, establishing a tradeoff between mobile receivers' location and performance, is introduced in terms of the asynchronous delays. Simulation results are presented in a representative scenario to demonstrate the performance gains offered by the proposed optimum transmit signal. The proposed scheme does not introduce any changes at the mobile receivers.     

A Differential Modulation Scheme for MIMO Links with Distributed Transmit Antennas

This letter proposes a differential en/decoding scheme for multiple-input multiple-output (MIMO) communication links with distributed transmit antennas, in which neither the transmitter nor the receiver knows channel knowledge. The proposed scheme is based on the layered differential space-time codes we present. Simulation results show that the bit error rate (BER) performance is nonidentical in different channel propagation delay cases. The optimum delay time for two transmit antennas system, for example, is about 0.6T_s (where T_s denotes symbol period) when the links achieve better performance.     

Degrees of freedom of MIMO interference channel with distributed space-time interference alignment

In the context of K-user MIMO interference channel (IC),achievable degrees of freedom (DoF) were investigated with distributed space-time interference alignment (DSTIA).By precoding with distributed current and outdated channel state information at the transmitters (CSIT),new tradeoff regions between achievable DoF and CSI feedback delay/frequency were achieved for MISO system.The impact of the number of transmit antennas on achievable DoF in the MISO system was analyzed,revealing that DoF results approach to the outer bound as the number of transmit antennas increases.Further,the impact of the number of receive antennas on achievable DoF was characterized,deriving the range of CSI feedback delay that preserves achievable DoF in the MIMO system.Theoretical and numerical analyses show that,the proposed DSTIA scheme can achieve better sum-DoFs by eliminating inter-user interference perfectly,tighten the gap between achievable DoF and outer bound,as well as improve the achievable rate of the system.